Growth of large-size tantalum nitride crystals for high-performace thermal conductive applications

The metallic theta-phase tantalum nitride (θ-TaN) has been predicted to have ultrahigh thermal conductivity (κ), making it suitable for cost-effective manufacturing of high-performance and high-temperature heat exchangers, heat pumps, and heating elements. The theoretical calculations suggest that a reduction of defect and grain boundary densities can enhance the room-temperature κ of polycrystalline θ-TaN. θ-TaN is typically obtained through the phase transition from the epsilon-phase tantalum nitride (ε-TaN) under high pressure and high temperature, and the grain size of θ-TaN obtained is comparable to that of ε-TaN, which is approximately 70 nm in the commerically available ε-TaN products. We discovered that the presence of Ta₂O₅ as the flux facilitates the growth of ε-TaN grains to micrometer sizes. By empolying the traveling solvent floating zone method, we obtained ε-TaN crystals with large grain sizes, which is suitable to be converted to the θ-TaN materials under high pressure and high temperature.